Nonlinear optical materials have recently been considered for use with optical devices such as a high-speed optical switch or a high frequency generator. In particular, those materials formed of a metal fine particle, a semiconductor fine particle or organic compounds having a nonlinear optical property, and a manufacturing method therefore have received attention in developing high-performance materials.
Conventional methods in this technical field include production of metal fine particle-dispersed glasses by a melt-quenching method (Appl. Phys. A., Vol. 47 (1988), p. 347). The method is based on a melt-quenching method, similar to a conventional method for filter-glasses, in which gold melted in a glass matrix is subjected to heat to precipitate gold fine particles.
Methods for producing gold colloid are also known (J. Opt. Soc. Am. B, Vol. 7 (1990), p. 790). In this method colloidal gold is formed from a reducing agent and a 0.01% aqueous solution of chloroauric acid.
A method for producing a metal fine particle-doped matrix is also known (Japanese Unexamined Patent Publication No. HEI-239535). This method includes two different ways in which a metal fine particle produced from light irradiation and/or heat treatment is doped in a matrix, and a metal fine particle-producing compound is doped in a matrix.
The use of cut-off filter glasses formed of borosilicate glass and CdS.sub.x Se.sub.1-x dispersed therein is also disclosed (J. Opt. Soc. Am. B, Vol. 73 (1983), p. 647). The cut-off filter glass is made by melting a mixture of CdS.sub.x Se.sub.1-x and raw materials for making borosilicate glasses in a platinum crucible at about 1000.degree. C.
The above methods of manufacturing nonlinear optical materials comprising a metal or semiconductor fine particle have the following problems.
(1) The metal fine particle-dispersed glass
The melt-quenching method restricts the kinds of metals available for use. Further, at most, only about 10.sup.-6 to 10.sup.-5 vol. % of the metal can be dispersed since the solubility of metal to glass is low.
High temperatures of 1000.degree. C. or more are needed to precipitate a fine particle from the metal dispersed in the glass.
A glass containing one kind of metal element permits an optical signal process at the wavelength of the plasmon absorption band other metal. Thus, the glass does not permit a multiple signal process.
(2) The gold colloid
It is difficult to increase the concentration of gold colloid. When the concentration of gold colloid increases more than 10.sup.-6 vol. %, the colloid begins to cohere. Even when the concentration becomes low, the colloid is less stable for long time use. With time, the composition of the solution gradually changes, or the particle diameter of the colloid increases. Further, as stated above, a glass containing one kind of metal element permits an optical signal process at the wavelength of the plasmon absorption band of the metal. Thus, the glass does not permit a multiple signal process.
(3) The semiconductor fine particle-dispersed glass
By the melt-quenching method, a part of the semiconductor components evaporates in the melting process, which changes the composition of the semiconductor. With a glass containing just one kind of a semiconductor, the third order nonlinear optical effect appears, allowing an optical signal process only when the glass absorbs light having a wavelength in the band gap of the semiconductor. In addition, the glass does not permit multiple signal processing.
(4) Production of a metal fine particle by light irradiation and/or heat treatment
Light irradiation provides insufficient reduction, and it restricts the kinds of compounds used to provide the intended metal fine particle. With use of heating and light irradiation, the fine particle which was produced by the irradiation grows, and the mean particle diameter and the deviation increase.